To express the density of oxygen, which is 0.001429 grams per cubic centimeter, in scientific notation, we need to write it in the format \( a \times 10^n \), where \( a \) is a number between 1 and 10, and \( n \) is an integer.
The number 0.001429 can be rewritten by moving the decimal point three places to the right. When we do this, we increase the exponent of 10 by 3, making it negative because we are moving to the right (toward smaller values).
So, \( 0.001429 = 1.429 \times 10^{-3} \).
Thus, the correct answer is:
1.429 x 10^-3